Best definition I've landed on: customer marketing is everything that drives value from and for existing customers post-sale. Sales brings them in; customer marketing helps them stick around, grow, and advocate.
The pillars you listed are mechanisms and they all serve three things: retention, expansion, advocacy.
Lifecycle, education, and comms mostly drive retention and product adoption.
Community and advocacy programs drive advocacy (and feed retention).
Executive engagement is expansion and senior-buyer relationships. VoC feeds all of them.
All of this travels well outside marketing because retention, expansion, and advocacy are how CS, product, and execs think about the customer base too.
Happy to compare notes on how I've seen orgs map team structure to those three outcomes.